Process Simulation of Laboratory Wastewater Treatment via

Article pubs.acs.org/IECR

Process Simulation of Laboratory Wastewater Treatment via Supercritical Water Oxidation Xiuqin Dong, Yaqi Wang, Xuqing Li, Yingzhe Yu,* and Minhua Zhang* Key Laboratory for Green Chemical Technology of Ministry of Education, R & D Center for Petrochemical Technology, Tianjin University, Tianjin 300072, China S Supporting Information *

ABSTRACT: Laboratory wastewater has neither a regular discharge cycle nor a regular discharge quantity, and its compositions are so complex that they are rather difficult to dispose of. The purpose of this study is to set up a small laboratory wastewater treatment plant, and it mainly focuses on the treatment of organic wastewater in the laboratory via supercritical water oxidation (SCWO). The process conditions optimized experimentally were the following: 440 °C, 26 MPa, longer than 70 s of residence time, hydrogen peroxide as oxidant with a 2.6 times excessive rate. The reaction kinetics equation was obtained through study of the degradation reaction of laboratory wastewater in supercritical water. The wastewater treatment process was simulated with the program PRO/II, and a relatively complete design scheme of a laboratory wastewater treatment process by SCWO was proposed from such aspects as the mass balance, heat balance, and equipment calculation. At the same time, an equipment prototype was established, and thus, a small laboratory wastewater treatment plant could be set up.

1. INTRODUCTION Wastewater treatment has become a significant issue for chemical processes on account of natural laws and rules to maintain a cleaner environment.1 Laboratory wastewater mainly means the wastewater discharged during research, education, and industrial and agricultural product development by all kinds of laboratories such as education research institution laboratories, industrial research and development (R&D) laboratories, analysis laboratories, medical and health testing laboratories, etc. In addition, it also includes washing water of containers and equipment, cooling water, cleaning groundwater, disinfecting water, the wastewater in the research process, and so on. Laboratory wastewater has neither a regular discharge cycle nor a regular discharge quantity, and its components, especially the heavy metal elements and other special toxic pollutants, are so complex that they are rather difficult to dispose of by the biological treatment process in sewage treatment plants. This paper mainly focuses on the organic wastewater, which contains common organic solvents, organic acids, ethers, organophosphorus compounds, phenols, oils, greases, etc., which are the most difficult to treat with various compositions and concentrations. At present, reports of laboratory wastewater treatment technologies are rare and the existing processes employed are physical,2 biochemical,3,4 and chemical oxidation methods5 and the combination of the aforementioned methods.6 Supercritical water (SCW) is a unique medium above the thermodynamic critical point (374 °C, 221 bar)7,8 with the property that nonpolar compounds and organics can be completely miscible in SCW.9 Supercritical water oxidation (SCWO) is an advanced water oxidation technology first developed by the American scholar Modell10 in the mid-1980s, and it has been rapidly developed since then. Attracting the attention of many researchers, this technology is expected to become an effective method to deal with organic waste11 © 2014 American Chemical Society

because of its advantages of high efficiency, environmental friendliness, and thorough organic removal. Numbers of enterprises and research institutions have carried out the study of the applications of SCWO technology. The studies are mainly divided into two categories: one is the study of degradation of model pollutants with supercritical water oxidation. Phenol and phenolic substitute compounds are the most common type of model pollutants that have been mentioned above. A large number of literature works and books have studied the degradation factors,12,13 reaction kinetics,14,15 and reaction mechanism16,17 of degradation of these compounds by SCWO. Another type of research is aimed at the actual wastewater, including papermaking wastewater,18 chemical production wastewater,19 pharmaceutical industry wastewater,20 war industry wastewater,21 etc. A novel method in SCWO research is using advanced process simulation technology to simulate the process. Cocero et al.22 used the program ASPEN to simulate a pilot experimental device with the capacity of 2 m3/h, whose nhexane removal rate was 99.9% under the reaction conditions of 650 °C and 23 MPa, and the results agreed well with the experimental values. Lavric et al.23 also conducted the simulation of 5 wt % hexane solution treatment process, which showed that both the Brayton cycle (CBC) and Rankine cycle (ORC) could be self-sufficient in energy and the latter was more realistic. Applying process simulation to the supercritical water oxidation process will promote the development of new technologies and play a positive role in amplifying the scale of and industrializing SCWO technologies. Received: Revised: Accepted: Published: 7723

December 30, 2013 April 9, 2014 April 16, 2014 April 16, 2014 dx.doi.org/10.1021/ie4044339 | Ind. Eng. Chem. Res. 2014, 53, 7723−7729

Industrial & Engineering Chemistry Research

Article

Raw materials first flow into the liquid buffer via highpressure plunger pump to ensure the smooth flow and, then, enter the preheater. After that, the materials go into plug-flow reactor to be heated and pressurized to supercritical conditions, under which organics rapidly react with oxidant. The liquid enters the quencher to be cooled. The pressure of system should be controlled by the counterbalance valve, and then, the mixture flows into gas−liquid separator. Finally, the separated liquid is collected and the separated gas is emitted continuously. The feedstock is automatically controlled by plunger pump. Liquid preheater provides heat by single electric stove wires, and the heating system of the reactor consists of a main heater and three auxiliary heaters to ensure a constant temperature in the reactor during the experiment. The counterbalance valve can control the pressure of system, which fluctuates within ±0.2 MPa. 2.1.3. Suitable Process Conditions. The process of supercritical water oxidation is difficult to implement in engineering due to the conditions of high temperature, high pressure, and strong oxidative atmosphere which need equipment with demanding requirements. So, this study tries to reduce the operation pressure and temperature and extend residence time under the premise of fully degrading the organics. This study examined the influence of such factors as temperature, pressure, the selection and dosage of oxidant, and residence time on the laboratory wastewater treatment by SCWO, respectively. According to the experimental results (shown in Figure S1−4 in the Supporting Information) and the principles of optimizing process conditions, the reaction pressure is set to 26 MPa, hydrogen peroxide is chosen as oxidant with a 2.6 times excessive rate, and residence time longer than 70 s. Beginning with low temperature ranging from 400 to 480 °C, the effect of oxidation degradation of the laboratory wastewater is investigated. The experimental results are shown in Table 2 (TOC stands for total organic carbon). Qualitative analysis of gaseous products under suitable conditions indicates that CO2 has been found in the products and neither of CO nor NOx has been detected, which is consistent with the results of Xu et al.24

This research is thus threefold: First, the process conditions of laboratory wastewater treatment by SCWO were researched to select appropriate conditions. Second, the reaction kinetics of the degradation was studied to lay the basis for the entire process simulation and engineering design amplification. Finally, the prgoram PRO/II was used to simulate the wastewater treatment process, and a relatively complete design scheme of a laboratory wastewater treatment process by SCWO was proposed from such aspects as the mass balance, heat balance, and equipment calculation, which could assist us in setting up a small laboratory wastewater treatment plant.

2. MATERIALS AND METHODS 2.1. Experiment. 2.1.1. Compositions and Concentrations of Wastewater. This study focused on organic synthetic laboratories. Methanol, ethanol, acetone, n-hexane, ethyl acetate, etc., are commonly used and phenol, nitrobenzene, etc., are common organic synthetic raw materials in these laboratories. Furthermore, phenol and nitro compounds are typical representatives which are the most difficult to degrade. So, the aforementioned materials were chosen as the compositions of laboratory wastewater. Specific concentrations are shown in Table 1. Table 1. Wastewater Compositions and Concentrations compound

concentration/mg·kg−1

methanol ethanol acetone ethyl acetate n-hexane phenol nitrobenzene

800 1000 800 800 50 500 300

2.1.2. Experimental Device and Procedure. In Figure 1, the experimental equipment used in this study is given. The unit consists of a high pressure plunger pump, liquor preheater, reactor, quencher, gas−liquid separator, counterbalance valve, etc.

Figure 1. Flowchart of supercritical water oxidation system upset: 1−liquid storage tank, 2−plunger pump, 3−liquid buffer, 4−check valve, 5−liquor preheater, 6−reaction tube, 7−quencher, 8−sampler, 9−filter, 10−counterbalance valve, 11−vapor−liquid separator, 12−liquid tank. 7724

dx.doi.org/10.1021/ie4044339 | Ind. Eng. Chem. Res. 2014, 53, 7723−7729


Article

Table 2. Experimental Results experiment

temperature °C

removal rate of nitrobenzene %

nitrobenzene mg·kg−1

TOC mg·kg−1

1 2 3 4 5 international emission standard

400 420 440 460 480

99.30 99.33 99.43 ∼100 ∼100

2.1 2.0 1.7

67.6 29.8 11.36 11.2 10.04 30

3.0

The simplex method was used to conduct the optimization computation because of its easy convergence and low requirements of initial values, despite the low calculation speed.25 With MATLAB programming, the value of S was reduced by modifying the parameters with the simplex method and adjusting the initial value with the symmetry principle. The desired parameter values are the ones when the S value meets the convergence criteria. The reaction kinetics equation of nitrobenzene degradation via supercritical water oxidation is

To ensure that laboratory wastewater can meet the standard after the process, based on the experimental results of the process, the proper process conditions determined are shown in Table 3. Table 3. Optimal Technological Conditions temperature °C

pressure MPa

residence time s

excessive rate of H2O2

440

26

>70

2.6

r = 8.851 × 106exp( −6.935 × 104 /RT )C NB1.545CO2 0.449

Where, r is the reaction rate of nitrobenzene in moles per liter per minute and Ci denotes the concentration of the i component in moles per liter. The dynamic model obtained by experimental data regression must be subject to the statistical test and analysis of residual distribution to judge the reliability and accuracy of the model. In Table 4, the statistical results of the kinetic model

2.2. Kinetic Model. The reaction kinetics of nitrobenzene degradation by SCWO was studied, which was the typical representative of the materials most difficult to degrade, in order to further research the law of the reaction, further understand supercritical water oxidation process, and provide the guidance for design, optimization, and control of the process in the industrial application. A reaction kinetics equation with power exponents was used to conduct this research because the products of the organic pollutants treated by SCWO are too complex to describe with elementary reactions. The mathematical model of nitrobenzene degradation reaction kinetics is FNB0 dXNB s dz

Table 4. Statistical Results of the Kinetic Model of Nitrobenzene

= A exp( −Ea /RT )[NB]0 a (1 − XNB)a ⎛ ⎞b νO2 [NB]0 XNB⎟ ⎜[O2 ]0 − νNB ⎝ ⎠

The initial conditions are z = 0, XNB = 0, [NB] = [NB]0, [O2] = [O2]0. In addition, the density of supercritical water is different from that in normal condition and varies with changes in temperature and pressure. Therefore, instead of directly using the original experimental data, the original experiment data should be processed with the reference to the PVT relationship of reaction system. And then concentration and flow rate of nitrobenzene and oxygen under reaction conditions were calculated. The kinetics data are given in Table S1 in the Supporting Information. The fourth-order Runge−Kutta equation was chosen to determine the parameters of A, Ea, a, and b in the kinetics equation. Experimental data of nitrobenzene conversion and a residual sum of squares of model calculation were used as the objective function of parameter estimation:

result 20 4 0.931 81.145 4.44 5.61

of nitrobenzene are given. From this table, it is obvious that R2 > 0.9, F > 10F0.05, F > 10F0.01, and all the δi are less than 10%, which suggest that the kinetic equation is accurate. 2.3. Process Model. 2.3.1. Determination of Thermodynamics Method. The selection of the thermodynamics method has a direct influence on the precision and accuracy of the analysis, process, optimization, and equipment calculation results. So the selection of the appropriate thermodynamic method is the key to the simulation. The system studied here contained water, a small amount of organics, O2, CO2, N2, etc. and was in supercritical state with high temperature and high pressure. The PR equation could be used to calculate fluid properties of supercritical state. Furthermore, the equation called PRM (PR-modified Panagiotopoulos−Reid) which introduces four adjustable interaction parameters is of higher calculation accuracy. So the PRM equation was chosen for the models in this system such as the reactor, heat exchanger, pump, counterbalance valve, and mixer while the thermodynamics model of vapor−liquid equilibrium used the NRTL equation that was applicable to a water system. 2.3.2. Selection of Calculation Method. All streams convergence and direct iteration convergence were adopted in this study for the simplicity of supercritical water oxidation

q

S=

item experiment groups number of parameters to be estimated correlation coefficient R2 F test value Fα (α = 0.05) Fα (α = 0.01)

cal exp 2 − XNB ) ∑ (XNB i=1

Where, S stands for the residual sum of squares, q is the number cal exp of parameters to be estimated, XNB and XNB represent calculated conversion and experimental conversion of nitrobenzene, respectively. 7725



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Figure 2. Process flowchart of laboratory wastewater treatment using SCWO.

Figure 3. Flowchart of amplified laboratory wastewater treatment using SCWO.

(4) Other: The pump and valve modules were also used in simulation. 2.3.4. Model Verification. In order to verify the accuracy of thermodynamics method and models that were selected in the SCWO process, the partial physical properties of the supercritical water were calculated, including density, enthalpy, and thermal capacity under constant pressure. The results of calculated and reported supercritical water density are shown in Table S2−4 from the Supporting Information. It can be seen from the tables that most of the calculation results agree with those in the literature, while only the part at low temperature and high pressure shows large relative deviation. Therefore, the selected model can be used to simulate a reaction system within the experiment scale and guide the engineering design. 2.3.5. Parameter Calculation. According to the optimal process conditions determined by experiment, calculation parameters are as follows: The feed pressure of wastewater and hydrogen peroxide is 0.1 MPa, and the temperature is 20 °C. Methanol, phenol, etc. contained in laboratory wastewater can react rapidly and are degraded easily, while nitrobenzene is the most difficult to degrade. So the pollutants after disposal can meet the national discharge standard as long as nitrobenzene does. Therefore, nitrobenzene is the only pollutant to be considered in the wastewater of the simulation feedstock. The concentration of wastewater is 300 mg/kg, hydrogen peroxide is chosen as the oxidant, and the excess rate is 2.6. After reaction, the concentration of nitrobenzene should be less than 3 mg/kg,

process. The direct iteration method is known as a successive substitution method which is the most direct, simple, and quite stable method, but its convergence speed is slow. The sequence method in the process simulation was the Minimum Tear Streams. It is the most commonly used method due to having the least torn streams and the least variables associated with those streams. 2.3.3. Establishment of Unit Models. The laboratory wastewater oxidization process mainly consists of heat exchange, reaction, and separation. The following unit models were selected to build the process: (1) Reactor: Organics, water, and oxygen are miscible for little mass transfer resistance in supercritical water, so the reaction is under homogeneous condition. The tubular reactor in the experiment could be simulated by a plugflow reactor. (2) Heat exchanger: For heating and cooling streams, or the heat exchange between two streams, the simple heat exchanger module (Simple HX) in PRO/II software was chosen to calculate a simple heat balance, not involving the specific structure of a heat exchanger. Zone analysis along the direction of temperature change was conducted, and the temperature of streams in the middle area was calculated to check driving force generated by temperature difference in heat exchangers. (3) Vapor−liquid separator: This is a flash unit in PRO/II, which is applicable to both VLE and VLLE calculation, and can be used to conduct balance calculation of any defined parallel conditions. 7726



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Table 5. Mass Composition of Main Steams in Existing Laboratory-Scale Process stream

S1

S2

S3

S4

S5

S6

S7

S8

water CO2 N2 nitrobenzene O2 T/°C p/MPa flow/kg/h

98.5800 0.0000 0.0000 0.0300 1.3900 20.00 0.10 0.3000

98.5800 0.0000 0.0000 0.0300 1.3900 20.29 26.00 0.3000

98.5800 0.0000 0.0000 0.0300 1.3900 440.00 26.00 0.3000

98.5910 0.0643 3.41 × 10−03 2.24 × 10−05 1.3413 440.00 26.00 0.3000

98.5910 0.0643 3.41 × 10−03 2.24 × 10−05 1.3413 20.00 26.00 0.3000

98.5910 0.0643 3.41 × 10−03 2.24 × 10−05 1.3413 25.46 0.10 0.3000

1.5123 1.6017 0.2600 6.58 × 10−09 96.6260 22.15 0.10 3.38 × 10−03

99.6968 0.0467 4.85 × 10−04 4.29 × 10−05 0.2559 22.15 0.10 0.2966

Table 6. Mass Composition of Main Steams in Amplified Process stream

S1

S3

S5

S6

S7

S8

S9

S11

S12

water CO2 N2 nitrobenzene H2O2 T/°C p/MPa flow kg/h

0.0000 0.0000 0.0000 0.0000 100.0000 20.00 0.10 1.4100

99.9700 0.0000 0.0000 0.0300 0.0000 20.00 0.10 100.0000

98.5800 0.0000 0.0000 0.0296 1.3904 20.19 26.00 101.4100

98.5800 0.0000 0.0000 0.0296 1.3904 420.00 26.00 101.4100

98.5800 0.0000 0.0000 0.0296 1.3904 440.00 26.00 101.4100

98.5910 0.0634 3.36 × 10−03 2.54 × 10−05 1.3424 440.00 26.00 101.4100

98.5910 0.0634 3.36 × 10−03 2.54 × 10−05 1.3424 20.00 26.00 101.4100

1.5125 1.5801 0.2564 3.94 × 10−09 96.6510 22.16 0.10 1.1430

99.6974 0.0461 4.78 × 10−04 2.56 × 10−05 0.2559 22.16 0.10 100.2671

3. CALCULATION RESULTS 3.1. Calculation Results of Existing Process. The main stream data by simulation for the exiting laboratory-scale process are listed in Table 5. It is clearly seen from calculation results, the concentration of nitrobenzene is less than 0.5 mg/ kg after reaction under certain conditions. And the removal rate of nitrobenzene is 99.86%, which is in excellent agreement with the results obtained from experiments. 3.2. Calculation Results of Amplified Process. The main stream data of amplified process by simulation are included in Table 6. It is obvious from results that nitrobenzene removal rate under the process conditions can reach 99.91%, and the concentration after reaction is lower than 0.3 mg/kg, which meets the national emission standard. The load of heat exchanger E0 is 265 200 kJ/h, and the heat needed by the cold stream is provided by the hot stream of the reactor outlet. The heat supplement for preheater E1 is 11 000 kJ/h, that is, 3.056 kW.

that is to say, the nitrobenzene removal rate should be over 99%. The reaction temperature is supposed to be constant at 440 °C for a low concentration of raw materials and minimal heat effect, although it is an exothermic reaction. The stream pressure of the reactor inlet is 26 MPa, and the residence time in the reactor is supposed to be 70 s. Calculation is conducted with the kinetic equation determined by experiment, r = 8.851 × 106 exp(−6.935 × 104/RT)CNB1.545CO20.449. The stream flows into quencher after reaction, and the temperature decreases to 20 °C. The operational pressure of the vapor−liquid separator is 0.1 MPa, and adiabatic flash is applied. The wastewater pump inlet pressure is atmospheric pressure, while the outlet pressure is 26.0 MPa. The stream pressure decreases to 0.1 MPa after the counterbalance valve. 2.3.6. Process. The existing experimental process simulated by PRO/II is shown in Figure 2.The scale of calculation for laboratory wastewater treatment is 0.3 kg/h. The length of the reactor is 0.369 m, and the inner diameter is 12.8 mm. Amplification and energy optimization have been conducted on the basis of the existing process. The amplified technological process is shown in Figure 3. Laboratory wastewater is mixed with hydrogen peroxide before flowing into thermal coupling heat exchanger E0. The heated materials reach the specific temperature through preheater E1, and then, organics are degraded in tubular reactor R1 where organics rapidly react with oxidant. The stream enters thermal coupling exchanger E0 to be cooled, passes counterbalance valve V1, and then flows into vapor−liquid separator F1 to continuously collect the liquid; the vapor is emitted. The scale of wastewater treatment is amplified to 100 kg/h. The length of reactor is 4 m, and the inner diameter is 80 mm. After calculation, the reactor volume is 20.42 L. Energy optimization also has been employed to the existing process. The cold stream temperature reaches 420 °C through heat exchanger E0 and becomes 440 °C through preheater E1. The rest of the unit operation parameters are the same as those mentioned in section 2.3.5.

4. DESIGN OF THE PLANT A vertical storage tank with volume of 2.50 m3 and DN 1400 × 1600 is used to store wastewater for a day and a night. For the need of high pressure in supercritical water oxidation reaction, a plunger pump is chosen as the feed pump. The maximum flow is twice the normal flow, J5 type is chosen, the flow is 200 L/h, and the highest pressure is 40.0 MPa. The maximum flow of the hydrogen peroxide pump is 10 L/h, and the highest pressure is 40.0 MPa. Fluid state, residence time, and inlet temperature are the same before and after amplification of the reactor26 which is at a constant temperature of 440 °C. On the basis of the aforementioned principles, the calculated reactor effective volume is Vr = 20.42 L. L/D ≥ 50 is set to ensure the fluid in the reactor stays in the state of plug flow, and Re > 10 000 is set to ensure turbulence in the reactor. The finally determined reactor diameter is 80.0 mm, and the length is 4.0 m. A doublepipe heat interchanger is chosen to ensure that the fluid is in the turbulent state which facilitates the heat transfer. The hot stream flows into the tube while the cold stream flows between the tubes. An electrical heating apparatus with adjustable power 7727



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Table 7. Equipment Information Table operation conditions equipment code

equipment name

V-01

liquid storage tank

vertical type, 2.5 m3 DN 1400 × 1600

P-01

wastewater pump

metering pump, flow 200 L/h

P-02

metering pump, flow 10 L/h

E-00

hydrogen peroxide pump heat exchanger

R-01

tubular reactor

V-02

vapor−liquid separator

specification and structure

operational medium lab organic wastewater lab organic wastewater hydrogen peroxide

double-pipe heat interchanger, A = 17.2 m2 inner pipe Φ 32 × 3.5, outer pipe Φ 32 × 3.5 effective volume 20.42 L DN 80 × 4000 vertical type, 1.50 m3 DN 1000 × 1600

water, organics, N2, O2, etc. water, O2, and organics water, O2, N2, etc.

temperature°C room temperature room temperature room temperature pipe: 20−420 shell: 440−50 440 room temperature

pressure MPa 0.1 0.1 0.1 pipe: 26 shell: 26 26.0 0.1

kinetics equation determined by the experiment. Material balances and heat balances of the supercritical water oxidation devices with a capacity of 100 kg/h were conducted. The concentration of nitrobenzene was lower than 0.3 mg/kg, and the removal rate was 99.91% after the reaction, which met the national discharge standard. (4) The main equipment involved in the process was selected, and a relatively complete design scheme of the laboratory wastewater treatment process by SCWO was established.

is equipped outside the double-pipe heat interchanger. There is no hot stream to preheat the feed at the beginning of the reaction, so the electrical heating apparatus is needed. The electrical heating apparatus is used to supply only the complementary heat after the equipment runs normally. A stainless steel tube of Φ 32 × 3.5 and material type 316 is chosen as the heat exchange tube, which meets the strength requirement after the thickness calculation and check, and a stainless steel tube with Φ 57 × 3.5 is selected as the outer tube. A heat transfer area of 17.17 m2 is needed with 15% allowance, so the length of heat exchanger is 210 m. Separation capacity is selected to be 1.0 m3/(m3h) to ensure the effectiveness of vapor−liquid separation, and the separation volume of the vapor phase is 1.05 m3 according to the vapor flow rate. The liquid residence time is set to 5 min to make sure the vapor is released completely and the liquid level of the separator is maintained. After calculation, the volume is 86 L, and the total volume is 1.17 m3 with a liquid proportion of 0.70 in the separator. It is determined that the volume is 1.5 m3 and the size is DN 1000 × 1600 with reference to the related design manuals.27 The equipment information on laboratory wastewater treatment process by supercritical water oxidation is summarized in Table 7.

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ASSOCIATED CONTENT

S Supporting Information *

Effects of reaction temperature, pressure, H2O2 dose ratio, and residence time on removal efficiency of laboratory wastewater components (Figure S1−4, respectively). Data of nitrobenzene supercritical water oxidation kinetics (Table S1). Comparison of the calculated and reported supercritical water density, capacity, and enthalpy (Table S2−4, respectively). This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (Y.Y.). *E-mail: [email protected] (M.Z.).

5. CONCLUSIONS This study focused on the degradation law of the main pollutants in laboratory wastewater by supercritical water oxidation technology. PRO/II software was used to simulate and optimize the process, and the design principles of the main equipment were established; thus, the following conclusions were obtained: (1) An experiment investigated the reaction temperature, pressure, selection of oxidant and its excess rate, residence time, and other factors in the laboratory. Using hydrogen peroxide as oxidant, a 2.6 times excess rate, a temperature of 440 °C, a pressure of 26 MPa, and a residence time longer than 70 s suitable degradation process conditions of the system were found. The contents of organic pollutants and TOC met the discharge standard GB8978-1996 after the laboratory wastewater treatment under the process conditions. (2) Through the study of reaction kinetics, the reaction kinetics equation of the nitrobenzene degradation by SCWO under experimental conditions is r = 8.851 × 106exp(−6.935 × 104/ RT)CNB1.545CO20.449. (3) PRO/II was used to simulate the process of laboratory wastewater treatment by supercritical water oxidation on the basis of the process conditions and the

Notes

The authors declare no competing financial interest.

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REFERENCES

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